Get a giant list of interview questions and make a mental note of some of them that you are struggling with and ask the consultant, junior doctor etc. about how they would answer it, it can often focus your mind on your own answer.
For example I have known for the past 5/6 years I wanted to study medicine...but I could never answer the question "why do you want to be a doctor?" When, I asked some doctors this I realised exactly why I wanted to and even why I struggled answering the question. It was really useful...asking about medical stuff is not that useful.